1. Field of the Invention
This invention generally relates to the field of coupled transmission line, and more particularly, to a complementary-conducting-strip coupled-line (thereinafter called CCS CL).
2. Description of the Prior Art
The thin-film microstrip (thereinafter called TFMS) is the most popular transmission line (thereinafter called TL) for realizing monolithic microwave integrated circuit (thereinafter called MMIC). When TFMS is designed for backward-wave couplers, however, the directivity is generally poor because the even- and odd-mode phase velocities of the coupled TFMSs are not equal. Furthermore, due to spacing limitation between edge-coupled TFMSs, which is restricted by the capability of the complementary metal-oxide semiconductor (thereinafter called CMOS) technology, limit the tight coupling achievable to about 3.0 dB over λg/4 sections. The broadside-coupled structures are often used and caused the super loss of TLs on the silicon or GaAs substrate with very thin layer of inter-media-dielectric (thereinafter called IMD).
In view of the drawbacks mentioned with the prior art of coupled TLs, there is a continuous need to develop a new and improved CCS CL that overcomes the shortages associated with the prior art. The advantages of the present invention are that it solves the problems mentioned above.